Nutritional Evaluation On Of Micro-elements Of Soil And Wheat Grain In Major Wheat Production Regions Of China

Microelements are essential for maintaining the growth and metabolism of plants and human.Currently,around 3 billion people in the world suffered from the hidden hunger due to insufficient intake of microelements such as iron（Fe）and zinc（Zn）.Wheat,a kind of staple food crop in China,is an important source of human body’s intake of microelements.It is of great importance to clarify the regional distributions and influencing factors of soil and grain microelements concentrations,for better understanding the soil micronutrient supply abilities,and achieving higher wheat yield and quality in major wheat production regions of China,and optimizing wheat micronutrient management and maintaining human health.During 2016 to2021,a successive 6-year wheat field survey was conducted by collecting plant and soil samples from 17 major wheat production regions in China.Available iron（Fe）,manganese（Mn）,copper（Cu）and zinc（Zn）concentrations were determined to evaluate their abundance and deficiency status in soils.Grain microelements concentrations were determined to evaluate wheat nutritional status according to the human micronutrient intake standard of Chinese Nutrition Society and health risk assessment method of United States Environmental Protection Agency,as well as the dietary habit of Chinese residents.Also,the contributions of main soil factors on available Fe,Mn,Cu and Zn of soil and grain microelements concentrations were quantified in this study.The main results are as follows:1.Soil available Fe concentration was ranged from 1.8 to 611.9 mg kg^-1,with an average of 49.1 mg kg^-1,and 8.9%of soil samples of lower available Fe than the threshold of Fe deficiency(4.5 mg kg^-1).Soils with low available Fe were usually observed in Shanxi,Shaanxi and Gansu provinces in Northern and Northwestern wheat production regions,while high Fe soils were found in Southwestern and middle and low Yangtze River wheat production regions.Soil available Mn concentration was ranged from 0.1 to 176.2 mg kg^-1,with an average of22.1 mg kg^-1,and 6.9%of samples exhibited lower available Mn than the threshold of Mn deficiency(5.0 mg kg^-1).Manganese-deficient soils were mainly distributed in Shanxi,Shaanxi,Gansu and Inner Mongolia provinces in Northern and Northwestern wheat growing regions,and soils with high and very high available Fe often occurred in Southwestern and middle and lower Yangtze River wheat production regions.Soil available Cu concentration was ranged from 0.1 to 10.8 mg kg^-1,with an average of 1.9 mg kg^-1,and only 1.8%of samples had lower available Cu than the critical value of Cu deficiency(0.5 mg kg^-1).Soil available Zn concentration was ranged from 0.1 mg kg^-1 to 26.0 mg kg^-1,with an average of 1.4 mg kg^-1.Available Zn in 14.3%of soil samples was lower than the threshold of Zn deficiency(0.5mg kg^-1).Zinc-deficient soils were mainly found in Shanxi,Shaanxi,Gansu and Inner Mongolia provinces in Northern and Northwestern wheat production regions,and high Zn soils were mainly observed in Yunnan and Guizhou provinces in Southwestern wheat growing regions.2.Random Forest and Pearson correlation analysis showed that p H was the most important factor affecting soil available Fe with a very significant negative correlation（r=-0.734）between them.The importance of soil nitrate nitrogen,ammonium nitrogen and available potassium on available Fe were low.For soil available Mn,the p H was still the most important influencing factor,secondly was ammonium N and available Fe.Soil total N and available Zn had the low effect on available Mn.For available Cu in soil,the available Fe produced the most primary influence with a very significant positive correlation（r=0.355）between them.For available Cu,soil available N,phosphrus and potassium produced the insignificant influence.For soil available Zn,the importance was less than 0.2 from all soil factors.The available phosphorus and Cu produced the high importance on available Zn,and both of them with available Zn have the significant positive correlation（respectively as r=0.251、r=0.257）.3.Average grain Fe concentration of wheat in China was 43.8 mg kg^-1,grain Fe concentration in 72.9%of the samples were smaller than the Fe lower limit of 50 mg kg^?1,and grain Fe concentrations were smaller than the Fe upper limit of 140 mg kg^?1 for all the samples.The concentrations of Fe were generally deficient,except for part regions of Heilongjiang and Guizhou province.Average grain Mn concentration was 43.0 mg kg^-1,grain Mn concentratoions in only 4.1%of samples were smaller than the Mn lower limit of 22 mg kg^?1and were larger than the Mn upper limit of 50 mg kg^?1 in 23.7%of samples.Part samples from southern Anhui and Heilongjiang province were exceeded the recommended Mn upper limit.Average grain Cu concentration was 4.6 mg kg^?1,grain Cu concentration in 7.6%of samples were smaller than the Cu lower limit of 3 mg kg^?1 and no sample was exceeded the Cu upper limit of 10 mg kg^?1.Average grain Zn concentration was 31.4 mg kg^?1,grain Zn concentration in 85.8%of samples were smaller than the Zn lower limit of 40 mg kg^?1 and only 4.1%was exceeded the Zn upper limit of 50 mg kg^?1.The concentration of grain Zn was generally deficient,except for part regions of Southern of Anhui province and Chongqing Municipality.Average grain boron（B）concentration was 1.2 mg kg^?1,grain B concentration in 29.2%of samples was smaller than the B lower limit of 0.8 mg kg^?1 and no sample was exceeded the B upper limit of 10 mg kg^?1.Grain B deficiency was mainly observed in southwestern wheat production region.Average grain molybdenum（Mo）concentration was 0.5 mg kg^?1,grain Mo concentration in 18.8%of samples were smaller than the Mo lower limit of 0.2 mg kg^?1 and only 0.4%of samples was exceeded the Mo upper limit of 2 mg kg^?1.Grain Mo deficiency mainly occurred in southwestern and the middle and lower Yangtze River wheat growing region.4.Based on the random forest and pearson correlation analysis,the soil p H was the most important factor affecting grain Fe,the next was soil available potassium,and there was a very significant negative correlation（r=-0.242）between p H and grain Fe.For grain Mn,the soil p H also produced the most primary influence,followed by the soil available Mn.A very significant negative correlation（r=-0.526）was found between p H and grain Mn.For grain Cu,the soil p H was the most important influencing factor,next was the soil available phosphorus.A significant negative correlation（r=-0.077）was observed between p H and grain Cu.For grain Zn,the soil available Fe produced the most important influence with a significant negative correlation（r=-0.070）.For grain B,the soil available Fe was the most important influencing factor,next was the soil available Zn.There was a significant negative correlation（r=-0.206）between grain B and available Fe.For grain Mo,the soil available Mn produced the most important influence with a significant negative correlation（r=-0.474）,next was the soil available p H.To sum up,the large regional variation was found in soil available Fe,Mn,Cu,and Zn concentrations of wheat fields in China.Deficiencies of soil available Fe,Mn and Zn were the serious problem on calcareous soils in the northern part,and the higher supply of these microelements occurred in the southern part,while almost all the wheat fields were not identified as Cu-deficient soil in China.Among the investigated soil properties,soil p H was the most important influencing factor on available Fe and Mn.Available Fe contributed to the highest Cu availability.Available phosphorus,followed by Cu,was found to the the leading factors on soil available Zn in major wheat production regions of China.The large regional variations was also found in the grain micronutrient concentrations of major wheat production regions in China.The concentrations of Fe and Zn were generally low in most regions,and the concentrations of B and Mo were insufficient in some areas,while the concentration of Mn was high,and the concentration of Cu was located in the recommended concentration ranges.For the investigated soil properties,soil p H was the most important influencing factor on gain Fe,Mn amd Cu;and available phosphorus and Cu contributed to the gtreatest to grain Zn;available Fe and Zn contributed to the largest to grain B;and soil available Mn,followed by p H,was found to the leading factors for soil grain Mo in major wheat production regions of China.In the furure,regulating soil p H,and applying the microelement fertilizers of Fe,Zn,B and Mo according to soil nutrient status,and avoiding the negative effects produced by high grain Mn contention are important measures to achieve green and efficient wheat production.